1. Field of the Invention
The present invention relates to a microbial engineering technique useful for production of amino acids and, more specifically to a method for producing L-lysine or L-arginine by fermentation. The present invention also relates to a microorganism useful for the production method.
2. Background Art
L-amino acids such as L-lysine, L-glutamic acid, L-threonine, L-leucine, L-isoleucine, L-valine and L-phenylalanine are industrially produced by fermentation using microorganisms belonging to the genus Brevibacterium, Corynebacterium, Bacillus, Escherichia, Streptomyces, Pseudomonas, Arthrobacter, Serratia, Penicillium, Candida, and the like. Bacterial strains isolated from nature or artificial mutants of these bacterial stains are often used in order to improve productivity of these microorganisms. Furthermore, various techniques have been disclosed for increasing L-amino acid production from these stains by enhancing the activity of L-amino acid biosynthetic enzymes using recombinant DNA techniques.
L-amino acid production has been considerably increased by breeding of microorganisms such as those mentioned above and the resulting improvements m the production methods. However, in order to respond to further increases in demand in the future, the development of methods which provide more efficient production of L-amino acids at a lower cost are clearly still necessary, and therefore, still represent a need in the art.
Methanol is a known fermentation raw material which is available in large amounts at a low cost. Methods for producing L-amino acids by fermentation using methanol are known and include methods using microorganisms that belong to the genus Achromobacter or Pseudomonas (Japanese Patent Publication (Kokoku) No. 45-25273), Protaminobacter (Japanese Patent Laid-Open Publication (Kokai) No. 49-125590), Protaminobacter or Methanoinonas (Japanese Patent Laid-open Publication (Kokai) No. 50-25790), Microcyclus (Japanese Patent Laid-open Publication (Kokai) No. 52-18886), Methylobacillus (Japanese Patent Laid-open Publication (Kokai) No. 4-91793), Bacillus (Japanese translation of PCT international application Patent (Kohyo) No. 3-505284 (WO90/12105)) and so forth. The inventors of the present invention have developed methods for producing L-amino acids by breeding bacteria belonging to the genus Methylophilus and Methylobacillus using artificial mutagenesis and recombinant DNA techniques (International Publication WO00/61723; Japanese Patent Laid-open Publication (Kokai) No. 2001-120269).
In recent years proteins have been identified that have a function of specifically secreting an L-amino acid to the outside of a cell or microorganism, as well as the genes which encode these proteins. In particular, Vrljic et al. have identified a gene involved in the secretion of L-lysine from a Corynebacterium bacterium to the outside of a cell (Molecular Microbiology 22:815-826 (1996)). This gene was designated as lysE, and it was reported that L-lysine producing ability of Corynebacterium bacteria could be improved by enhancing the expression of this gene in the bacteria (International Publication WO97/23597). It is also known that production of several kinds of L-amino acids can be improved by increasing expression amounts of amino acid secreting proteins in Escherichia coli (Japanese Patent Laid-open Publication No. 2000-189180). For example, it has been reported that production of cystine, cysteine, and so forth can be improved by enhancing the expression of ORF306 gene in Escherichia coli (European Patent Laid-open Publication No. 885962).
However, there have been no reports to date on improving the L-amino acid production by enhancing their secretion during fermentation of methanol-assimilating bacteria. Furthermore, no amino acid secretion gene that can exhibit secretion activity in methanol-assimilating bacteria has been reported.